1. Field of the invention
The invention relates to a new class of diamond-like solid state materials, especially films and coatings thereof, and methods of their manufacture. The materials include a clusterless diamond-like nanocomposite structure which contains interpenetrating networks of a diamond-like matrix stabilized by hydrogen, and a silicon glass-like network stabilized by oxygen, and contains, in addition to carbon, hydrogen, silicon and oxygen, and other elements, especially any or a combination of transition metals of 1b-7b, 8 groups of the periodic table.
2. Description of the prior art
Diamond-like carbon (dlc) films are unique materials which possess many of the technologically important properties of diamond, such as high hardness, high chemical stability, electrochemical and wear resistance, high electrical resistivity and high thermal conductivity. The amorphous nature of dlc films, unlike diamond, allows the synthesis of extremely uniform, smooth, nonporous, thin films with thicknesses as low as 10 nm and a low coefficient of friction. While the synthesis of diamond films require substrate temperatures in excess of about 800.degree. C., dlc films can be synthesized at close to room temperature. Further, dlc films can be deposited on virtually any substrate material. As a result of these factors, a number of coating applications of dlc films have recently been developed.
Dlc films are formed by a variety of low pressure processes such as d.c., r.f. or microwave plasma decomposition of hydrocarbon gases, laser ablation of graphite and low energy carbon ion beam deposition.
A common factor in most of these processes is the bombardment of the growth surface by low energy ions in the range of about 100-1000 eV. However, there are serious problems related to the synthesis and application of dlc films. Key problems are low adherence to a number of useful substrates, high residual stress levels (particularly at the dlc/substrate interface) and a low fatigue threshold. Further, the high electrical resistivity of dlc films, limits their field of applications largely to protective coatings and some optical applications. A key problem is the low thermal stability of dle films. Complete graphitization occurs at temperatures above 600.degree. C.
Recently, extensive work has been devoted to a new class of carbon-base micro-composites (R. d'Agostino, ed., Plasma Deposition, Treatment, and Etching of Polymers, Academic Press, San Diego, 1990). The term "composite" is used to stress that the main microstructural feature of this class of materials, distinguishable, for example, by electron microscopy, is the existence of regions of one of the constituents dispersed randomly in the matrix of another. At low concentration of metallic elements in an organic matrix, (dielectric regime) the microstructural inhomogeneities (small metallic inclusions) are randomly dispersed in the organic matrix. As the metal concentration is increased, the metal inclusions grow and form a maze network (transition regime). At the percolation threshold, which is characterized by macroscopic connectivity of the inclusions, most of the characteristics of the composite material change abruptly. By increasing the concentration of metal atoms further, a metallic regime is reached and the material can be characterized as a metallic continuum with dielectric inclusions. In this respect, plasma polymerized polymer/metal films differ fundamentally from plasma polymerized organometallic films, where the metals are usually dispersed as chemically bonded atoms.
A particular class of carbon-based microcomposites which have been investigated, are based on the inclusion of heavy metals, e.g. W, in an hydrogenated amorphous matrix. Usually, metals form carbides in such films. Weissmantel et al.(J. Vac. Sci. Technol. Vol. A 4, p. 2892, 1986.) fabricated amorphous carbon films containing extremely small metal clusters. However, upon annealing at temperatures above 1000K, a segregation of small carbide or small metal crystallites was observed. The presence of only a small amount of the metal (.about.3 at %) appeared to influence the microstructure of the metastable carbon matrix, which exhibited a sharp drop in microhardness and resistivity.